Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include devices with neural stimulation (NS) capability. Other examples include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. Further examples of implantable medical devices include implantable diagnostic devices, or implantable drug delivery systems.
Neural stimulation can be useful to treat neurological impairment of physiological systems of a patient such as the bladder, the upper airway, and the heart. Vagus nerve stimulation has been proposed to treat breathing disorders, gastrointestinal motility, eating disorders, obesity, anorexia, gastrointestinal tract disorders, hypertension, coma, and epilepsy.
Most implantable devices are processor controlled. Typically, the processor executes instructions contained in firmware to flexibly implement functions required by the device. Implementing functions of an IMD in firmware can have some disadvantages. As the number of functions performable by an implantable device increases, the processor may have to be constantly executing instructions to respond to external events and device initiated events. This can result in a large amount of battery power being consumed by the device. Also, events may result in electrical stimulation circuits drawing a large amount of battery power.